A video signal for use as input to an electronic video display consists of a number of sub signals, each sub signal representing color information for different areas of the picture, and the color information is represented by basic colors, i.e. RGB (red, blue, green) or YUV (luminance & chrominance).
If the viewer wants to amplify the contrast in a picture and thereby obtain a better light output from a display, this is done by boosting a weak signal (i.e. 50%) to nominal (i.e. 100%). There may still be 100% peaks in the signal that will now reach 200% of the permitted maximum level.
A problem with contrast amplification is that there is a contrast limit corresponding to the electronic video display or the D/A converter in the signal processor, meaning that the electronic video display is adapted to receive a limited range of input signals and the D/A converter in the signal processor is adapted to deliver a limited range of output signals.
These signal processors therefore comprise a variety of limiters for converting the signal range of the video signal to a signal range being within an acceptable range.
An embodiment of such a limiter is described un U.S. Pat. No. 5,349,390. U.S. Pat. No. 5,349,390 describes a device for reducing the amplitude range, which includes a first contrast reduction device receiving a picture signal for providing a contrast reduced picture signal; the contrast reduction device only reduces the contrast of the picture signal over the entire area when the picture signal exceeds a given first threshold (e.g. 90%) for relatively large areas. The picture signal processor also includes a second contrast reduction device, which supplements the first contrast reduction device and which provides the contrast reduced picture signal by immediately reducing the contrast of a too bright part of the first contrast reduced picture signal as soon and as long as an instantaneous amplitude of the first contrast-reduced picture signal exceeds a given second threshold (100%). This implementation is built with analog circuitry and is based on a feedback loop. Further an analog implementation is very cumbersome and noise sensitive, and it is hard to make adjustments for an optimum response. Further the picture might lose details in the bright areas because of the clipping of the small peaks.